Cellular radiotelephone systems are divided into cells to permit the systematic reuse of radio channels. A plurality of cells are often joined into a singular cellular system in which the entire geographical extent is defined as a single service area with separate service provided by two service providers. These two cellular providers are mandated by law and involve two bands of frequency for radiotelephone channels; one, the wireline band (A band), is assigned to a first service provider and the other, the non-wireline band (B band), is assigned to a second service provider.
When mobile radiotelephones are handed off in passage from one service area to another, during continuance of a call, (and become roamers) the same band (A or B) of frequency is normally retained for the balance of the call. When a roaming mobile telephone, initiates a new call within a new service area, it is programmed or otherwise operative to seek out or prefer the same A or B band it uses in its home territory. Some mobile radiotelephone units may permit manual selection of A or B bands by the user, but in general the mobile radiotelephone units are preset to at least prefer just one band regardless of its service area location.
Many service providers have acquired cellular systems in many differing cellular service areas. These areas are often nearby or adjacent to one another and the service provider has the opportunity to combine the various cellular systems into a large virtual single cellular service area. However the service provider may own A band channels in some service areas and B band channels in the balance of the service areas. Hence a typical customer, using one band in his home service area, may pass into an adjacent service area where his provider provides the other band and due to the mobile radiotelephone's propensity for remaining with a singular band becomes a customer of a competing service provider. This partially negates the advantage of acquiring a plurality of service areas to gain economies of scale in providing mobile radiotelephone service. Various systems have been proposed to accommodate the traveling cellular subscriber's mobile radio telephone. A system proposed in U.S. Pat. No. 4,972,455 provides a multi-bandwidth cellular telephone to allow use in differing cellular telephone systems such as a cellular telephone system and a mobile telephone system. Use in differing systems requires the use of different telephone numbers. Another arrangement disclosed in U.S. Pat. No. 5,020,091 contemplates the assignment of multiple telephone numbers to the radio telephone for use in different cellular radiotelephone systems. Another arrangement disclosed in U.S. Pat. 4,677,653 has a mobile phone unit that includes a plurality of telephone numbers. The assignment of added numbers to a mobile radiotelephone unit add to the cost of operation of that phone unit.